1. Field of the Invention
Embodiments of the present invention relate generally to computer graphics applications and more specifically to reducing memory bandwidth requirements in an anti-aliasing operation.
2. Description of the Related Art
Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Anti-aliasing processing typically occurs during the rendering stage of graphics processing and is generally used to diminish artifacts such as “jaggies,” which are stair-like lines that appear at places in an image where there should be smooth, straight lines or curves. To achieve high quality anti-aliasing results without significantly scaling up the memory footprint and bandwidth requirements, one approach is the virtual coverage anti-aliasing (“VCAA”) technique, which is discussed and claimed in the U.S. application titled, “System and Method for Virtual Coverage Anti-Aliasing,” referenced above. Basically, the VCAA technique extends the concept of multi-sample anti-aliasing by weighing different color contributions of the real samples, also referred to as real subpixels, of each pixel to determine the color of the pixel. To influence the aforementioned color contributions, the VCAA technique creates and utilizes a set of virtual samples for each pixel. Unlike a real sample, which is uniquely associated with at least Z-data and color data, a virtual sample does not have such association. Instead, a virtual sample contains information associating with or pointing to one or more real samples based on geometric primitive coverage. Such information is also referred to as “virtual coverage information” or “virtual sample coverage information.” Because the virtual samples mainly provide the affiliation information to the real samples and also the additional coverage information of one or more geometric primitives on the pixel but not the Z-data and color data, they are represented by significantly fewer bits than the real samples.
The virtual samples with the aforementioned affiliation and coverage information generally are stored in the frame buffer. This affiliation and coverage information is needed and potentially updated when performing, for example, Z-testing on the real samples. Thus, to either update or retrieve these virtual samples, the frame buffer needs to be accessed. Such accesses consume frame buffer bandwidth, which is somewhat limited in typical graphics processing unit (“GPU”) designs, and also the resources of the requesting component. Repeated accesses of the frame buffer for virtual sample information can thus limit overall system performance.
As the foregoing illustrates, what is needed is a way to efficiently manage the accesses of the virtual samples to further improve the overall performance of anti-aliasing operations performed by a GPU.